1. Field of the Invention
The present invention relates to an inflator for an inflating type safety system of a vehicle, and in particular, to an inflator which can reliably discharge a gas for inflating an air bag and does not have a complicated structure, and in which a gas to be discharged is clean, i.e. containing substantially no combustion residue.
2. Description of Related Art
In the development of inflators for an inflating-type safety system for motor vehicles, hybrid inflators using both a pressurized gas and a gas generating agent has been attracting attention, and such a hybrid inflator inflates an air bag by discharging a pressurized gas in a sealed state.
Such an inflating-type safety system for vehicles is required to activate reliably as needed, and naturally, an inflator used therein is also required to activate reliably.
In particular, in an inflator using a pressurized gas, it is necessary to reliably activate a mechanism for releasing the pressurized gas charged and sealed in an interior of a housing in order to assure its operation reliability. In many cases, a rupturable plate is used as a sealing member for sealing a pressurized gas, and the sealed state is broken by rupturing the rupturable plate. Then, the pressure in a pressurized gas accommodation chamber is raised by a flame (or heat, hereinafter, used in the same manner) or a gas generated by combustion of a solid gas generating agent. The rupturable plate is broken by a projectile, an impact wave, a flame, a gas or the like generated at a time of activation of an igniter. Among them, it is particularly desirable to use an impact wave, a flame, a gas or the like generated at a time of activation of an igniter for reducing weight of the inflator due to its a simple constitution, and there have conventionally been various proposals for the structures of such an inflator.
For example, a technique in which an inlet for guiding a combustion product (an impact wave, a flame, a gas or the like) generated by activation of an igniter, into an interior of a pressurized medium accommodation chamber, and an outlet for guiding a pressurized gas in the pressurized medium accommodation chamber to a gas discharging port or passage are covered by a single rupturable plate which is ruptured by activation of an igniter, is disclosed in U.S. Pat. No. 6,217,065. The disclosure thereof describes a state in which a rupturable plate is deformed to bulge towards the igniter by receiving pressure from the pressurized medium before activation. However, in the art disclosed in this document, only a peripheral portion of the rupturable plate is fixed by welding, and thus, a welding radius becomes necessarily large. As a result, even if the igniter is activated, the rupturable plate is not reliably ruptured in that it must substantially change its original shape to be bulged or deformed toward the opposite direction.
Further, U.S. Pat. No. 6,062,599 discloses an inlet and an outlet opening in communication with a pressurized gas chamber covered by a single rupturable plate by welding the rupturable plate at two portions and scoring the rupturable plate to form fragile portions. As a result, manufacturing cost is increased since an extra welding step is required, and it is necessary to provide the fragile scored portions in the rupturable plate.
In inflators using pressurized gas, it is desirable to discharge the gas efficiently in order to inflate an air bag rapidly at a time of activation, and therefore it is important that an interior structure of an inflator housing is designed to obtain an efficient gas flow in the housing. Particularly, in a hybrid inflator using a flame or a gas generated by combustion of a solid gas generating agent, it is important to obtain an effective gas flow in view of efficiently using a flame or a gas generated by combustion of the gas generator.
Further, since a gas generated by combustion of the gas generating agent at a time of activation of the hybrid inflator has a high temperature, desirably, the hybrid inflator is formed such that a gas generated by combustion of the gas generating agent is not discharged directly, for improving a safety at activation. Then, a solid combustion product (combustion residue) generated by combustion of the gas generating agent has also a high temperature and there is a concern that an air bag (a bag body) may be damaged when the gas is discharged directly into the air bag. Therefore, it is desirable that such a combustion residue is prevented from directly flowing out of the housing with a flow of an operating gas for inflating the air bag. In other words, desirably, a gas to be discharged outside the housing will be clean, including little residue.
Since an inflator having a complicated structure increases the number of manufacturing steps and manufacturing cost, and an inflator having an increased volume causes inconvenience due to increased space requirements, it is necessary to avoid complicated inflator structures and increased size thereof.
However, with respect to inflators for inflating type safety systems for vehicles which activate air bags effectively, namely which not only inflate air bags to predetermined sizes in predetermined times, but also secure reliability of operation or activation if required, and that facilitate manufacturing, there is still room for development.